1. Field of the Invention
The present invention relates to a rotary head drum of an inner rotary head drum system.
2. Description of Related Art
A cassette type magnetic recording and reproducing apparatus using a rotary head drum is recently reduced in size notably while being enhanced in performance and quality. Its mechanism and rotary head drum are required to be smaller in size, and hence the rotary head drum of an inner rotary head drum system is employed more widely.
Referring to the drawings, a conventional example of rotary head drum is described below. FIG. 10(a), (b) are side views of a prior art rotary head drum. FIGS. 12(a), (b) are schematic diagrams of the tape path in a magnetic recording and reproducing apparatus, FIG. 12(a) being a plan view and FIG. 12(b) being a side view.
In the tape path shown in FIGS. 12(a), (b), a tape 31 wound on a reel 201 is helically wound around a rotary head drum 1 at a specified lead angle by a specified angle, and it is transferred at a constant speed through collaboration of a pinch roller 71 and a capstan 72 to record and reproduce. A plurality of loading posts 70 are drawn out from a mouth 203 of a cassette 2 for helical winding of the tape 31 around the rotary head drum 1. A specified tension is applied to the tape 31 in the rotary head drum 1.
Herein, in particular, in the case of a portable appliance such as a VTR with a built-in camera, in order to keep the entire appliance compact in size, it is necessary to locate the rotary head drum 1 deeply into the mouth 203 of the cassette 2. However, the cassette 2 is provided with a dust lid 202, and this lid 202 interferes with the upper part of the rotary head drum 1. To prevent this interference, generally, the rotary head drum 1 is moved to a lower side of the mouth 203 so as to depart from the lid 202, but since the rotary head drum 1 projects largely from the lower side of the cassette, the thickness of the appliance is increased. Accordingly, to suppress the thickness of the appliance, a cut portion 111 is formed by cutting off the upper part of the rotary head drum 1 obliquely as shown in FIG. 12(b).
To cut obliquely the upper part of the rotary head drum 1, as shown in FIG. 10, an upper drum 12 is fixed coaxially on a lower drum 11, and an inner drum 13 mounting a head 21 at its lower end is disposed coaxially between the two drums (this is the so-called inner drum rotation constitution). The inner drum 13 is rotatably supported by a shaft and a bearing (not shown). The thickness of the inner drum 13 is about half of the tape 31. The rotating direction is rightward as shown in the drawing.
The lower drum 11 is provided with a lead 14 for guiding the tape path, and the tape 31 runs while contacting with the lead 14 at its lower end. The upper drum 12 has the cut portion 111, and its outer circumference is processed by lathe finishing.
Conventionally, as shown in FIGS. 11(a), (b), the diameters d1, d2, d3 of the cylindrical surfaces of the outer circumference (the tape path guide) in the lower drum 11, upper drum 12, and inner drum 13 are set all the same, or in accordance with the relation d2 greater than d3 greater than d1.
With the above construction, it is possible to suppress the surface area and the thickness of the tape path, but the following problems are created.
That is, as the tape 31 is wound around the rotary head drum 1, as shown in a sectional view of a floating condition in FIGS. 11(a)-(b), air is included between the tape 31 and the inner drum 13 along with rotation of the inner drum 13 by the viscous resistance of air, and the floating height reaches a maximum on the inner drum 13, and then declines sequentially on the lower drum 11 and upper drum 12. The floating height is almost zero micron on the upper drum, more than ten microns on the inner drum, and several microns on the lower drum. Thus, when the diameter of the upper drum 12 is equal to or larger than the diameter of the inner drum 13, the tape 31 is always in contact with the upper drum 12.
In such a state, the frictional force between the tape 31 and the upper drum 12 is large, and the tape tension increment after installation of the rotary head drum is large, and hence the tape running load increases, thereby leading to tape damage, or slip generation at capstan 72, or increased motor current.
The tape 31 is often coated with a surface treating agent such as lubricant on both sides in order to improve the running performance. However, in the running state in which the tape 31 is in contact with the upper drum 12, since a machining tool path in a direction vertical to the axial center is formed on the outer circumference of the upper drum 12, the surface treating agent on the magnetic surface side, and other sub-micron dust particles in the appliance or deposits on the tape may collect along the machining tool path and be deposited on the upper drum 12. As a result, the tape running resistance may be increased, or in a worst case, sticking may occur between the tape 31 and the upper drum 12 or inner drum 13, and tape running may be disabled, or the magnetic layer may be peeled away from the base film of the tape 31.
To solve the above problems, the present invention includes a lower drum having a first tape path cylindrical surface for guiding a tape-form recording medium helically at a lead angle a, an upper drum having a second tape path cylindrical surface, and fixed oppositely and almost coaxially on the lower drum, and an inner drum having a third tape path cylindrical surface of nearly the same diameter as the first tape path cylindrical surface of the lower drum, rotatably supported almost coaxially between the upper drum and the lower drum, and having a rotary head, in which the second tape path cylindrical surface of the upper drum is at the inner side of the first tape path cylindrical surface of the lower drum in a range of winding of the tape-form recording medium on the upper drum.
The present invention also includes a lower drum having a first tape path cylindrical surface for guiding a tape-form recording medium helically at a lead angle a, an upper drum having a second tape path cylindrical surface of nearly the same diameter as the first tape path cylindrical surface of the lower drum, and fixed oppositely and almost coaxially on the lower drum, and an inner drum having a third tape path cylindrical surface, rotatably supported almost coaxially between the upper drum and the lower drum, and having a rotary head, in which the third tape path cylindrical surface of the inner drum is at the outer side of the first and second tape path cylindrical surfaces in a range of winding of the tape-form recording medium.
Thus, according to the rotary head drum of the present invention, since contact with the tape on the upper drum is restricted, the tape running load is reduced, and it is possible to prevent tape damage, slip on the capstan, and increased motor current.
The present invention is a rotary head drum comprising a lower drum having a first tape path cylindrical surface for guiding a tape-form recording medium helically at a lead angle a, an upper drum having a second tape path cylindrical surface, and being fixed oppositely and almost coaxially on the lower drum, and an inner drum having a third tape path cylindrical surface of nearly the same diameter as the first tape path cylindrical surface of the lower drum, rotatably supported almost coaxially between the upper drum and the lower drum, and having a rotary head, in which the second tape path cylindrical surface of the upper drum is at the inner side of the first tape path cylindrical surface of the lower drum in a range of winding of the tape-form recording medium on the upper drum. Therefore, since contact with the tape on the upper drum is restricted, the tape running load is reduced, thereby preventing tape damage, slip on the capstan, and increased motor current.